The presence of particulate matter (i.e. dust) is a serious hazard with respect to the environment and in general, to the personal health and safety of individuals exposed to it. Examples of dust forming material include iron ores, coal and other friable (i.e. a material that is easily broken up into small pieces) materials. Said materials are heretofore referred to as dusting materials.
Dust can already be in existence or be produced as a result of mechanical operations such as mining, loading, transportation, storage and handling processes of dusting materials. Dust suppression, as used herein, is defined as the prevention or reduction of the amount of fine particulates airborne or suspended in the air.
There are chemical and mechanical methods for dust suppression. Mechanical methods include dust collection equipments such as filters and cyclones. They may capture entrained dust, induce dust to settle, ventilate the area where dust is formed, etc. Chemical methods include short and long term residual suppressants.
Long term residual dust suppressants control dust through the formation of a polymer or binder film over the dusting material. The film remains over said material after evaporation of the solvent (e.g. water). Water is included in long term residual suppressants in order to provide an even spreading of the composition on the dusting material and they usually include film-forming or tackifying resins.
One of the most common short term dust suppressants is water. One disadvantage of using this method lies on the fact that large quantities of water may be needed in order to fully wet the material. When used in coal, for example, it results in the decrease of its specific heating value. Another disadvantage is that water loses its effectiveness upon evaporation, thus it is not indicated for materials that are going to be transported for several days in opened carts. Additives such as surfactants and wetting agents may be used to improve properties of the composition. Examples of short term suppressants are described in Patent Application 20050085407, U.S. Pat. No. 6,124,366 and U.S. Pat. No. 5,409,626.
Foam suppressants form a layer over the dusting material and may be used to capture dust through its bubbles. As a result, the suppressant is only effective while the bubbles are present in the homogeneous layer.
Some currently available compositions are not immediately effective, therefore requiring an extended period of time for satisfactory performance. Other compositions include excessive aromatic or other materials such as high levels of organic solvents.
To avoid the many problems encountered in dust reduction and to provide better means for minimizing the amount of dust escaping to the environment, a large number of products and processes have been extensively described in the literature, ranging from the utilization of natural and synthetic polymers and also using mixtures and combinations of surfactants and organic solvents. For example, U.S. Pat. No. 6,372,842 relates to a method of using an aqueous composition or dispersion containing a water-soluble or water-dispersible synthetic polymer, made of acrylate esters and alkyl substituted acrylamide and modified with an organosilane, useful for dust control and other applications, like an agricultural spray composition.
Aqueous solutions are also described in U.S. Pat. No. 5,194,174 which relates to an improved non-viscous aqueous dust control solution which includes a polyvinyl alcohol and boric acid. Other examples include U.S. Pat. No. 4,417,992 and U.S. Pat. No. 4,801,635 and Patent Application WO 9100866.
Patent application US200440192789 provides a method for controlling dusting of material comprising the steps of: applying an effective amount of a composition comprising an alkylphenol ethoxylate surfactant, a polyglycol which can be glycerin, propylene glycol or a mixture thereof.
U.S. Pat. No. 4,264,333 describes a method wherein the coal is first coated with a wetting agent and then coated with an emulsion of crude coal tar in water containing a cationic emulsifying agent.
Wetting agents such as ethylene oxide may be used as described in U.S. Pat. No. 4,316,811 and U.S. Pat. No. 4,369,121
The use of ethoxylated alkyl phenols was described in U.S. Pat. No. 4,428,984, U.S. Pat. No. 4,737,305, U.S. Pat. No. 4,169,170.
The use of emulsions is described in U.S. Pat. No. 4,650,598 and U.S. Pat. No. 4,981,398.
Aromatic solvents may be used as described in U.S. Pat. No. 4,960,532 which relates to a dust suppressant composition comprising water and a thickening agent forming the dispersion medium and coal tar pitch and aromatic solvent forming the dispersed liquid. Said composition forms a resilient layer.
Patent Application US 20050045853 describes a method and composition for suppressing coal dust including a metal-containing compound mixed with any appropriate dust suppressant liquid.